Anal Cancer Staging

Staging will determine how far a cancer has spread in our body. 

The options for treatment and prognosis is based off the staging of the anal cancer.

Staging criteria

Tumors are classified according to the size and characteristics of the primary tumor (T), whether the cancer has spread to regional lymph nodes (N), and whether the cancer has metastasized, or spread, to distant areas of the body (M).

The American Joint Committee on Cancer uses a formal staging based on these three criteria:

  • T: Tumor size and an assessment on invasion of nearby organs
  • N: Describes the size, location, and/or number of lymph nodes affected by the cancer
  • M: The absence or presence of metastases to distant organs

Invasive anal cancer is curable in a number of patients, particularly when it is diagnosed early and tumors are small. 

Four stages of anal cancer

Your doctor uses information from your scans, biopsies and other medical and surgical procedures to assign your cancer a stage.  

Stage I: The tumor is 2 centimeters or smaller 

Stage II: Tumor is larger than 2 cm.

Stage IIIA: The tumor is of any size and the cancer has metatasized to the lymph nodes near the rectum or organs nearby including the vagina, bladder or urethra

Stage IIIB: The tumor is of any size and spread to the lymph nodes in the rectum, pelvis, and/or groin, and possibly to nearby organs.

Stage IV: The tumour is of any size and may have spread to the lymph nodes or nearby organs and has also spread to distant parts of the body.


PET/CT scans

PET/CT (positron emission tomography/computed tomography) scans of the chest and abdomen and pelvis to stage the cancer.

  • Provides images of the internal organs and other structures such as blood vessels and lymph nodes to determine whether your cancer has spread to other areas of your body
  • Prior to imaging, patients usually drink a barium-like solution to outline the contents of the gastrointestinal tract, barium is also inserted through a tube in the rectum, and contrast dye is injected intravenously to distinguish the vascular structures 
  • This test is commonly done to assess the inguinal and pelvic lymph nodes and presence or absence of distant metastases in the liver and lungs.

In some cases, an MRI of the pelvis is done, which is a different type of imaging that uses a large magnetic coil and may be helpful in detecting spread to nearby organs.

Endoanal Ultrasound

Another tool commonly used to stage anal cancers

  • Procedure where a probe is inserted into the anus and rectum and uses sound waves like sonar to generate images and structures of the anal canal
  • Helps detect perirectal lymph nodes and involvement of neighboring organs to the anus

Ultrasound also provides a good estimation of the depth of invasion of the tumor, whether it is limited to the submucosa or penetrates the sphincter muscle

Modified staging system

A modified staging system based on ultrasound findings has been proposed:

  • uT1 tumor is confined to the submucosa
  • uTa lesion only invades the internal anal sphincter
  • uTb lesion invades the external sphincter
  • a uT3 invades through the sphincter muscles into the perianal tissue
  • uT4 tumor invades neighboring structures.